Modal of Probability
Must & Must Not
A Long Beach City College
E-ESL Lesson
Introduction
This lesson is a part of the Modals Opus. In this lesson, the modal
of probability, must, will be explained. The negative of must, must
not, will also be examined. This lesson will be followed by interactive
quizzes.
As with all modals, must obeys the following rules.
-
Must is never conjugated.
-
Must is followed by the simple form of the verb.
Must & Must Not
The modal must can be very confusing. Must, as well as must not,
are usually used as modals of expectation or obligation. When must,
or must not, is used as a modal of probability, it means that the speaker
is not absolutely certain (he or she might be wrong). Must means
that the speaker is about 90% certain. Must not means that
the speaker is about 95% certain. Must and must not can be used in
the simple present tense, the present continuous tense, the present perfect
tense, and the present perfect continuous tense. The best way to
demonstrate these uses is with examples.
Simple Present Tense
Must and must not are used with the simple present tense to show probability
of a current situation. Grammatically, must and must not are followed
by the simple form of the verb. *Please remember that the simple
form of am, is, and are is be!
-
Teacher: Where is Maria?
Student: Maria must be sick. She
always comes to school.
The student is saying that Maria is probably sick. The student
does not know for certain if she is ill.
-
Boss: Why haven't we received the equipment?
Employee: It must not be ready yet.
The employee does not know that the equipment is not ready. This
is just one possibility. It is also possible that the shipping company
has lost it. The employee just does not know.
Present Continuous Tense
Must and must not are used with the present continuous tense to show
probability of a situation that is happen right now. Grammatically,
must and must not are followed by the word "be" and than the -ing form
of the verb.
-
Friend One: Why isn't Bob answering the door?
Friend Two: He must be sleeping.
Friend Two does not know for that Bob is sleeping. Friend Two
is guessing. It is also possible that Bob is listening to music with
headphones or any other number of things.
-
Friend One: Why isn't Raul's car in the parking lot?
Friend Two: He must not be working today.
Once again, Friend Two does not know for certain why Raul's car isn't
in the parking lot. It is possible that his car wouldn't start and
he took the bus.
Present Perfect Tense
Must and must not are used with the present perfect tense to show probability
of a situation that has already happened. Grammatically, must and
must not are followed by the word "have" and then the past participle form
of the verb.
-
Student One: Where are your books?
Student Two: I must have left them in the
classroom.
Student One and Student Two are talking about
a past action. Student Two is not certain. Student Two thinks
that he/she left his/her books in the classroom.
-
Teacher: Why did Fusae fail the test?
Student: She must not have studied.
The student is saying that Fusae probably did not study. The
student does not know this. This is just one possibility. It
is also possible that Fusae was not feeling well when she took the test.
The student just does not know.
Present Perfect Continuous Tense
Must and must not are used with the present perfect continuous tense
to show probability of a situation that has happened in the past at the
same time as another event. Grammatically, must and must not are
followed by the word "have" and then the word "been" and then the -ing
form of the verb.
-
Friend One: Why wasn't Julia at home last night when we stopped by
her house.
Friend Two: Her grandmother hasn't been feeling well. She must
have been visiting her.
Once again, Friend Two isn't certain. Friend Two doesn't know for
certain where Julia was.
-
Friend One: Why wasn't Vincent at your party last weekend?
Friend Two: He was sneezing a lot Thursday. He must not have
been feeling well on Saturday.
Friend Two thinks that Vincent was sick. Vincent may not have been
sick but this is the most probable answer.
Quizzes